Four groups of rats, ten rats in each group, being maintained on the feeding machine, were served 17 meals per day of either sucrose, glucose, starch or casein. All rats were given essential nutrients by gastric intubation. At the onset of the experiment the rats were inoculated with A. viscosus T-6 and the level of infection was monitored by FA and culturing techniques at least once every week. In all three carbohydrate groups the number of Actinomyces increased to about 50 percent of the total flora cultivable on blood agar. Whereas, in the casein group the prevalence of Actinomyces was not dectectable after 14 days.